The Anatomy of Jordy Mercer’s RBI Double

PITTSBURGH – Last week, as a guest on The Blue Dot Report podcast, Dr. Alan Nathan was posed the question, “Does understanding concepts about physics help one understand or enjoy the game more?”

Dr. Nathan’s response was:

“I really do look for things that are indicative of phenomena that I’ve studied, or I try to find new, interesting phenomena based on what I observe.”

With that in mind, it’s no surprise that Dr. Nathan was able to offer the following insight relative to Jordy Mercer’s RBI double (seen in the video above) in the 8th-inning of the Pittsburgh Pirates’ 4-1 win over the St. Louis Cardinals.

The funny thing is Mercer’s hit wasn’t even supposed to happen (if the Pirates’ plans had worked out). A failed suicide squeeze attempt earlier in the at-bat forced the Pirates to change their strategy, which allowed Mercer to swing the bat and bring home Gregory Polanco for an added eighth-inning insurance run.

Let’s take a look at how it happened…

With one out and runners at second and third, following Josh Harrison’s sacrifice bunt (oddly enough), Mercer started off the at-bat by taking a slider from Cardinals’ sinkerballer Seth Maness for ball one.

As discussed, Mercer then tried to lay down a suicide squeeze bunt on the second pitch of the at-bat with Francisco Cervelli charging home from third.

As we can see, it did not go as intended…

In taking a closer look at the pitch that resulted in the failed bunt attempt, give Mercer a little bit of sympathy. He was forced to bunt on a 87 mph sinker with a spin rate of 1,500 rpm’s and a spin axis of roughly 275 degrees that was located just below that strike zone – not the ideal pitch to lay down a bunt.

We can see in the sequence below how Mercer’s bat angle keeps changing as the pitch nears. He has the bat square in the third image, but by the final image he is lunging at the ball with the bat tilted down as the pitch sinks down out of reach.





Now, with two outs and Polanco moving up to third during the Cervelli rundown, the idea of any type of sacrifice was clearly out the window. So Mercer was back to his normal approach at the plate.

With the count now 1-1, Maness came back with a slider that missed low and inside. He then induced Mercer to swing and miss on a changeup that was well outside the strike zone, before coming back inside with another changeup that would have been strike three had Mercer not fouled it off.

Pitch Sequence
Maness versus Mercer pitch sequence

For the fifth pitch of the at-bat Maness decided to try the sinker again. But having already seen the pitch (and knowing that the sinker is Maness’ speciality), Mercer took the 87.4 mph pitch 341.5 feet in the opposite direction, launching the ball at 20.6 degrees with an exit velocity of 100.3 mph for an RBI-double.

Perhaps Mercer had success with the pitch since A) he had seen it before in the same at-bat B) it was only 0.5 mph faster than the other sinker and C) this sinker had a spin rotation of a little over 1,000 rpm’s as opposed to the first sinker, which had a spin rotation of 1,500 rpm’s.

Moreover, as Dr. Nathan pointed out, we can see how Mercer’s bat is tilted down and below the center of the ball at impact, which gave the ball the sidespin and slicing action it needed to keep drifting further and further away from Cardinals’ centerfielder Randal Grichuk.

Mercer Bat Angle

Another look from behind lets us see again how the bat is pointed straight down to the ground as it reaches impact.

Mercer Bat Angle 2

This at-bat is a nice study in how a player was able to mentally recover (after the failed bunt attempt) and use a pitcher’s best pitch (Maness’ sinker) against him. The fact that it involved a nice marriage of baseball and physics with Dr. Nathan’s excellent one-of-a-kind insight, only made it that much better.